In general, metal catalysts are frequently used in the hydrogenation system of aromatic compounds. Compared with other catalytic reactions using non-metallic catalysts, metal catalysts are not only clean but also have a low impact on the economy and the environment. In addition, noble metals such as palladium, ruthenium, rhodium, and platinum have been demonstrated to have high catalytic activities in a hydrogen atmosphere.
For example, Bayer Corporation published in the United States Patent Publication No. 2005 6,841,626B1 that a noble metal, such as platinum (Pt) and palladium (Pd), is used as a catalyst, SiO2 and Al2O3 as a catalyst carrier, and cyclohexane as a solvent to carry out the hydrogenation reaction of polystyrene. The hydrogenation reaction of polystyrene catalyzed by Pt/SiO2 catalyst at a pressure of 875 bar, and a temperature of 150° C. can obtain a hydrogenation rate of 98.4%. While the hydrogenation reaction of polystyrene catalyzed by Pd/Al2O3, a hydrogenation rate approaches 100% under a pressure of 100 bar at a temperature of 200° C.
In addition, Bayer Corporation mentioned in China Patent No. 101,815,575 issued in 2010 that the catalyst used in the gas phase reaction can catalyze the hydrogenation of nitrobenzene to become aniline. The method includes steps of mixing 106.4 mg palladium chloride (PdCl2), 6 ml hydrochloric acid (HCl), and 294 ml distilled water to obtain 300 ml palladium chloride acid (H2PdCl4). In step (a), the mixed solution of 15 ml H2PdCl4 and 31.5 ml water and 3.5 ml methanol was added 33.25 mg polyvinylpyrrolidone (PVP-40), refluxed at 80° C. for 3 hours. Next, in step (b), 0.6 ml tetraethoxysilane (TEOS) was mixed with 7 ml ethanol. Subsequently, the mixed solution in step (a) was stirred violently, and a mixture of ethanol-ammonia (NH3) was added therein, then the mixture of ethanol-TEOS was quickly added therein, too. After stirring overnight at room temperature, the precipitation was washed with ethanol, and Pd—SiO2 nanoparticles were obtained by centrifugation. In step (c), 0.43 g alcohol-polyethylene glycol ether (such as Marlipal) was dissolved in water to prepare an aqueous solution of Marlipal. Next, the Pd—SiO2 nanoparticles obtained in step (b) were dispersed in 40 g ethanol and heated to 30° C. Subsequently, the aqueous solution of Marlipal was added to 30° C. Pd—SiO2 solution, 0.45 ml zirconium n-butoxide was added therein and stirred for 4 hours. The liquid phase with dispersion was replaced by water. Then, the solids were obtained by calcining at 900° C. The Pd—SiO2—ZrO2 particles obtained in step (c) were stirred in 50 ml solution containing 1 mole sodium hydroxide (NaOH) for 3 hours, then centrifuged and washed with a solution containing 1 mole NaOH. Finally, Pd—ZrO2 was obtained after drying at room temperature.
Furthermore, Zhu et al. taught in Chinese Patent No. CN101289365 published in 2011 that 0.12 g nitrate tetra-ammine platinum (Pt(NH3)4(NO3)2) and 7.4 g hexahydrate cobalt nitrate (Co(NO3)2.6H2O) were dissolved in 200 ml deionized water, and 3.5 g of the SiO2 carrier was added. After stirring for 2 hours, the mixture is dried in a water bath at 95° C., and then calcined at 550° C. to obtain a catalyst. The catalyst was placed in a reactor having a mixed atmosphere of hydrogen and nitrogen with a flow rate at 10 ml/min and 40 ml/min, and the benzene was fed with a flow rate at 0.5 ml/hrs. The conversion of benzene was 63% when the reaction temperature was 84° C.
However, the noble metals of the abovementioned hydrogenation catalysts are mounted onto aluminum oxide (Al2O3) or silica (SiO2), and the catalysts need to be separated from the required product by filtration after the reaction. It is difficult to recover the catalyst when the particles are too small to filter. Furthermore, since platinum is a very rare and expensive metal catalyst for general chemical reactions, the recovery of noble metal catalysts and recovery efficiency are important for reducing process costs to enhance efficiency and save resources.
It is therefore necessary to provide a hydrogenation catalyst and a method of manufacturing the hydrogenation catalyst capable of being recovered easily, in order to solve the problems existing in the conventional technology as described above.